Avocado rootstock named ‘Steddom’

ABSTRACT

A new and distinct  Persea americana  variety having strong resistance to  Phytophthora cinnamomi  when used as a rootstock. It is a relatively slow growing rootstock having a heavy yield, appearing to have a high yield/canopy volume ratio. ‘Steddom’ has a small degree of salt tolerance and appears to be an all-around, excellent rootstock with small stature and low vigor, making it desirable for high density or hedge-row avocado plantings.

Latin name of the genus and species: The avocado cultivar of this invention is botanically identified as Persea americana Mill.

Variety denomination: The variety denomination is ‘Steddom’.

BACKGROUND OF THE INVENTION

Avocado root rot is the limiting factor for the growth of avocados throughout the world. Avocado root rot is caused by the fungus Phytophthora cinnamomi, which attacks and kills the feeder roots of avocado trees. The resultant lack of roots causes the tree to eventually die from water stress. There are a number of varieties of rootstocks that have some tolerance to the disease. These varieties included ‘Duke 7’ (unpatented), the most commonly planted tolerant rootstock in the world; and ‘Thomas’ (U.S. Plant Pat. No. 6,628), another root rot tolerant rootstock. However, even with these rootstocks, growers must still use a variety of methods, including mounding, mulching and the applications of chemical fungicides, to keep the tress from dying in many soils. More resistant rootstocks are necessary to eliminate avocado root rot as a major disease threat.

Screening and Greenhouse Evaluation of Rootstocks

‘Steddom’ was identified and characterized using the following screening protocol. As it is difficult to breed avocados because only one in approximately one thousand flowers actually set fruit, plant breeding blocks of avocados were isolated to prevent out-crossing with susceptible rootstocks. The breeding blocks were made up of various combinations of selected rootstocks including, ‘Thomas’ (U.S. Plant Pat. No. 6,628), ‘Barr Duke’ (U.S. Plant Pat. No. 6,627), ‘G6’, ‘Duke 7’, ‘Duke 9’, ‘UC 2001’, ‘UC 2011’, ‘Toro Canyon’ (U.S. Plant Pat. No. 5,642), ‘Spencer’, ‘CR1-71’, ‘G 810’, ‘G 875’, ‘G 755A’, ‘VC 256’, and ‘Steyemarkii’. In order to synchronize blooming, attempts were made to girdle late-blooming varieties and spray early-blooming varieties with the pesticide Unicona-zole-P.

Initial screening was carried out by germinating seeds, which were harvested from the breeding blocks, in flats of vermiculite in the greenhouse. Phytophthora cinnamomi-infested millet was placed in rows along with the young roots of the test seedlings. After 8-10 weeks roots were evaluated and those with a high percentage of surviving roots were transplanted to soil mix incorporated with P. cinnamomi-infested millet. Rootstocks that survived this test were planted and grown in P. cinnamomi-infested soils. Survivors were examined more carefully for various types of resistance using asexual propagated material.

-   -   a. Root survival—Rootstocks were grown in typical California         avocado soils, inoculated with P. cinnamomi and evaluated for         growth, root length and percent healthy roots.     -   b. Root regeneration—Rootstocks were grown in soil inoculated         with P. cinnamomi, treated with Aliette to halt Phytophthora         root rot and evaluated for root regeneration.     -   c. Attraction to P. cinnamomi—Roots of the rootstocks were         placed in water baths with motile zoospores of P. cinnamomi. The         numbers of spores attracted to the roots were evaluated.

Rootstocks that performed well in the screening and greenhouse evaluations were further tested under field conditions.

Selection of ‘Steddom’

‘Steddom’ was developed at Riverside, Calif. The maternal parent is ‘Toro Canyon’ (U.S. Plant Pat. No. 5,642) avocado variety. The pollen parent is unknown. Specifically, the ‘Steddom’ rootstock variety was selected in 1994 from an agricultural operations land located Riverside, Calif. The fruit were collected from the avocado breeding blocks, the seed removed, and planted in vermiculite. The seeds were grown in a greenhouse. The plants were inoculated with the fungus Phytophthora cinnamomi. After showing tolerance to the disease, ‘Steddom’ was selected as a single plant for further testing. Budwood was collected from the plants and grafted to the stumps of adult avocado trees that had been cut down at Irvine Calif. The new varieties grew into trees which provided budwood for further testing. At least two ‘mother’ trees of the variety are growing in Irvine Calif., along with the germplasm. During screening and evaluation, ‘Steddom’, which was selected and originally designated ‘PP24’, distinguished itself from other varieties, including the maternal parent ‘Toro Canyon,’ by having a high tolerance against Phytophthora root rot. The properties of ‘Steddom’ were found to be true to type and transmissible by asexual reproduction.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a new and distinct avocado variety. ‘Steddom’ is an avocado tree having a rootstock that has a high tolerance against Phytophthora root rot. It is a relatively slow growing rootstock and that yields heavily, and has a high yield/canopy volume ratio. ‘Steddom’ has a small degree of salt tolerance and appears to be an all-around, excellent rootstock with small stature and low vigor. For these reasons it may be an excellent choice for high density or hedge-row avocado plantings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a eight-year-old top-worked tree of the ‘Steddom’ variety while growing in Irvine, Calif.

FIG. 2 illustrates typical mature foliage of the ‘Steddom’ variety with dimensions in centimeters shown at the bottom.

FIG. 3 illustrates typical flush foliage of the ‘Steddom’ variety with dimensions in centimeters shown at the bottom.

FIG. 4A illustrates typical inflorescence with dimensions in centimeters shown at the right and FIG. 4B illustrates typical inflorescence by itself.

FIG. 5 illustrates a typical external view of the fruit of the ‘Steddom’ variety, with dimensions in centimeters shown at the bottom.

FIG. 6 illustrates typical internal views of the fruit of the ‘Steddom’ variety, with and without the seed. Dimensions in centimeters are shown at the bottom.

DETAILED DESCRIPTION OF THE INVENTION

The following is a detailed description of the new ‘Steddom’ variety, which was taken from an approximately eight-year-old mature tree, with the exception as a rootstock for a specific scion when reference is made to root rot resistance and salinity tolerance. The tree is located in an experimental orchard in Irvine, Calif. and is grafted on a Persea americana seedling used as a rootstock.

The Royal Horticultural Society (R.H.S.) Colour Chart is used herein for the color description of the rind, seed, bark, leaf, flower, flesh color and other interest of the ‘Steddom’ avocado tree.

Trees, Foliage, and Flowers

-   Tree:     -   -   Growth habit.—Vigorous and upright when compared to the             rootstock ‘Thomas’.         -   Vigor.—Below are data on the vigor of ‘Hass’ grafted onto             the rootstock ‘Steddom’, as determined by trunk diameter             measurements from trees planted in an orchard with             Phytophthora cinnamomi in Escondido Calif.

TABLE 1 Trunk diameter (cm) Rootstock year 1 year 2 year 3 year 4 year 5 PP # 24. 2.37 3.98 7.07 8.60 11.23 ‘Thomas’ 2.44 4.29 6.75 8.40 10.84 Escondido Ca., with Hass scion

TABLE 2 Canopy volume (cubic feet) Rootstock year 1 year 2 year 3 year 4 year 5 PP # 24. 14.00 100.40 376.1 478. 1257 ‘Thomas’ 13.56  84.48 388.5 367. 1076 Escondido Ca., with Hass scion

-   -   -   Size.—Medium. The typical canopy size of a three year old             top-worked ‘Thomas’ is 388 cu.ft. By comparison the canopy             size of a three year old top-worked ‘Steddom’ is 376 cu. ft.             The tree is 610-915 cm in height when fully grown at the             orchard site in Irvine, Calif.

-   Branch:     -   -   Color.—The color of the one year old branch is yellow-green             (RHS 144C).         -   Smoothness.—The bark of a one year old branch is smooth.         -   Lenticels.—The lenticels of a one year old branch are             conspicuous.

-   Main stem:     -   -   Color.—Brown (RHS N 200D and 197A).         -   Texture of bark.—Corky.

-   Young shoot (flush):     -   -   Intensity of anthocyanin coloration.—Weak.         -   Anthocyanin coloration.—Orange-brown (RHS 172A).         -   Color.—Yellow-green (RHS 145C).         -   Conspicuousness of lenticels.—Medium.         -   Color of lenticels.—Red-purple (RHS 61A).         -   Size of lenticels.—1.0-3.0 mm long.         -   Concentration of lenticels.—+/−24 lenticels per square cm.         -   Color of upper side.—Yellow-green (RHS 146A).         -   Glossiness of upper side.—Medium.         -   Color of lower surface.—Green (RHS 139D).

-   Mature leaf:     -   -   Length.—18.0 cm.         -   Width.—7.0 cm.         -   Ratio length/width.—2.6.         -   Shape.—Lanceolate.         -   Color of upper side.—Green (RHS 143A).         -   Color of lower side.—Green (RHS 145B).         -   Glossiness of upper side.—Medium.         -   Prominence of veins on lower side.—Prominent and in relief.         -   Color of veins.—Yellow-green (RHS 151A).         -   General shape and cross-section.—Asymmetrically folded.         -   Reflexing of apex.—Present.         -   Color of petiole.—Yellow-green (RHS 144A).         -   Anise aroma.—Present.         -   Margin.—Undulation of margin is weak, and the leaf margin is             entire.         -   Leaf apex shape.—Acuminate.         -   Leaf base shape.—Lanceolate.         -   Length of leaf petiole.—Approximately 4.5 cm.         -   Diameter of leaf petiole.—Approximately 3.0 mm.         -   Leaf arrangement.—Upright.

-   Flower:     -   -   Bud size.—Approximately 5 mm in length and approximately 3             mm in diameter.         -   Bud shape.—Ovoid.         -   Bud color.—Yellow-green (RHS 152C).         -   Opening.—Belongs to group “A”, male opening (i.e. with             mature stamens) occurs in the afternoon, the flower closes             over night, and female opening (i.e. with mature pistil)             occurs the next morning; the flower's opening cycle lasts             20-24 hours.         -   Petals.—Borne in two whorls of three perianth lobes. The             petals possess entire margins and petal coloration is near             yellow-green (RHS 150B). Both the upper and lower petal             surfaces are near yellow-green (RHS 150B).         -   Stamen.—There are commonly nine fertile stamens with each             having two basal nectar glands that are grayed-orange (RHS             174A) in color and three staminodia. The anthers are             tetrathecal.         -   Pistil.—The single pistil with a slender style and small             stigmatic surface has one carpel with one ovule. The ovary             is superior.         -   Sepals.—There are 6 sepals which are approximately 4 mm in             length and approximately 2 mm in width, and the color of             both sepal surfaces is near yellow-green (RHS 151A).         -   Pedicel.—Commonly approximately 7 mm in length and             approximately 1.8 mm in diameter. The coloration is near             yellow-green (RHS 151A).         -   Peduncles.—Approximately 4.2 cm in length and approximately             5.0 mm in diameter. The coloration is near yellow-green (RHS             151A).         -   Number of flowers on inflorescence.—Approximately 185-205             flowers per inflorescence.         -   Fragrance.—Absent.         -   Bloom.—Bloom period at Riverside, Calif. experiment station             varies with cultural conditions. On average ‘Steddom’ has             been found to bloom from 1st of February through 20th of             March.             Fruit, Fruit and Production Characteristics

-   Fruit:     -   -   Length.—9.7 cm.         -   Width.—5.4 cm.         -   Ratio length/width.—1.8.         -   Weight.—78.9 grams.         -   Shape.—Pyriform, with the fruit apex being pointed with a             diameter of approximately 2.4 cm and the base being rounded             with a diameter of approximately 5.4 cm.         -   Color of skin (when ripe).—Green (RHS 141B).         -   Texture of skin.—Smooth.         -   Presence of longitudinal ridges.—Absent.         -   Thickness of skin.—Thin.         -   Adherence of skin to flesh.—Medium.         -   Main color of flesh.—Yellow-green (RHS 154D).         -   Color of intensely colored area of flesh next to skin.—Green             (RHS 141C).         -   Width of intensely colored area next to skin.—3.0 mm.         -   Conspicuousness of fibers in flesh.—Inconspicuous.

-   Seed:     -   -   Length.—4.5 cm.         -   Width.—4.0 cm.         -   Weight.—16.9 grams.         -   Shape (in longitudinal section).—Ovate.         -   Shape (in cross section).—Circular.         -   Color of seed coat (fresh).—Grayed-yellow (RHS 162B).         -   Cotyledon color.—Orange-white (RHS 159B).         -   Time of harvesting.—‘Steddom’ fruits ripen in September (in             Riverside Calif.).         -   Resistance to pests.—Strong resistance to Phytophthora             cinnamomi.         -   Tolerance to salinity.—Moderate.         -   Market use.—The fruit of ‘Steddom’ are not intended for             market use, but rather the variety is used as a rootstock             onto which commercial varieties, such as ‘Hass’ are grafted.

TABLE 3 ‘Steddom’ Rootstock Trials as of 2004 San Diego County Santa Barbara County Ventura County San Luis Obispo County

TABLE 4 Summary of the performance of the ‘Steddom’ avocado rootstock in Phytophthora-infested soil Health ranking/# Trials with health Yield ranking/# rootstocks in rating below 1.5¹ rootstocks in Rootstock trial trial (1 is best) (0-5; 5 = dead) trial (1 is best) San Diego Co. Location 1 1/4 + 1/4 Location 2  8/15 +  1/15 Location 3  5/13 + None Location 4 1/4 + 1/4 Location 5  7/10 +  3/10 Location 6 1/3 + 1/3 Ventura Co. Location 1  3/12 +  3/12 Location 2  9/10 +  2/10 Santa Barbara Co. Location 1  3/10 +  3/10 Actual yield Rated higher than ranking/# rootstocks ‘Thomas’² Rootstock trial in trial (1 is best) (control) San Diego Co. Location 1 None + Location 2 6/15 + Location 3 None + Location 4 None + Location 5 None + Location 6 None + Ventura Co. Location 1 None + Location 2 None - Santa Barbara Co. Location 1 None + ¹1.5 health rating is the value that we would assign to trees not meeting grower approval under field conditions. ²‘Thomas’ is considered the best commercial avocado rootstock for planting in Phytophthora-infested soil.

TABLE 5 Rootstock rating at Santana, Ventura County, August 2001¹ Tree rating Canopy Trunk No. (0-5; volume diameter trees Rootstock 5 = dead) (cu ft) (cm) dead ‘Steddom’ 0.80 a 13.89 a 1.92 a 1 ‘Merensky II’ 0.90 a 15.10 a 1.48 a 1 ‘Uzi’ 0.90 a 16.92 a 2.02 a 0 ‘Zentmyer’ 1.05 a 16.48 a 2.05 a 1 ‘G755A (Brokaw)’ 1.65 a  5.55 a 1.62 a 1 ‘Medina’ 1.90 a 12.66 a 1.70 a 2 ‘Berg’ 2.20 a 13.80 a 1.29 a 4 ‘McKee’ 2.35 a  9.05 a 1.52 a 1 ‘Duke 7’ 2.50 a 11.40 a 1.24 a 4 ‘Thomas’ 2.65 a 10.22 a 1.15 a 4 ‘G755 A (C&M)’ 2.75 a 11.66 a 1.49 a 2 ‘UC 2023’ 3.00 a  6.21 a 1.25 a 3 ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 6 Rootstock rating at Santana, Ventura County, November 2002. Two-year trial to-date. Tree rating Canopy Trunk Fruit rating (0-5; volume diameter (0-5; Rootstock 5 = dead) (cu ft) (cm) 5 = heavy) ‘Merensky II’ 0.17 d  72.27 abc  3.49 ab   0.78 bcd ‘Uzi’ 0.50 cd  69.64 abcd 3.64 a   2.50 a ‘Steddom’ 1.00 bcd 67.95 abcd 2.94 abc   1.70 abc ‘Medina’ 1.06 bcd 79.89 ab  3.26 ab  0.00 d ‘Zentmyer’ 1.50 bcd 81.44 a   3.19 ab   0.60 bcd ‘Duke 7’ 1.67 bcd  32.48 abcde 2.31 abcd   1.11 abcd ‘Berg’ 1.72 bcd  46.57 abcde 2.21 abcd  2.00 ab ‘McKee’  1.78 abcd 30.92 bcde 2.24 abcd  0.22 cd ‘G755A  2.30 abcd 19.98 de  1.90 bcd 0.10 d (Brokaw)’ ‘Thomas’ 2.60 abc 31.50 bcde 2.02 abcd  0.30 cd ‘UC 2023’ 2.95 ab  25.50 cde  1.41 cd  0.20 d ‘G755 A (C&M)’ 4.00 a  15.71 e   0.82 d    0.00 d. Tip burn Canker rating No. trees Rootstock rating (0-5) (0-5) dead ‘Merensky II’ 0.00 a 0.33 a 0/9  ‘Uzi’ 0.33 a 0.00 a 1/10 ‘Steddom’ 0.25 a 0.00 a 2/10 ‘Medina’ 0.75 a 0.00 a 1/9  ‘Zentmyer’ 0.38 a 0.63 a 1/10 ‘Duke 7’ 0.38 a 0.38 a 3/9  ‘Berg’ 0.17 a 0.83 a 3/9  ‘McKee’ 0.43 a 0.29 a 2/10 ‘G755A (Brokaw)’ 0.29 a 0.14 a 3/10 ‘Thomas’ 0.17 a 1.00 a 4/10 ‘UC 2023’ 0.00 a 0.00 a 5/10 ‘G755 A (C&M)’ — — 8/10

TABLE 7 Tree rating August 2001 Tree rating Canopy Trunk diameter Rootstock (0-5; 5 = dead) volume (cu ft) (cm) ‘Thomas’ 0.00 a 2.00 a 22.91 a ‘Parida’ 0.12 a 1.08 b 15.77 b ‘Steddom’ 0.24 a 0.95 b 16.82 b ‘Spencer’ 0.50 a 1.84 a 24.53 a ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 8 Tree rating, July 2001 Tree rating Canopy volume Trunk diameter Rootstock (0-5; 5--dead) (cu ft) (cm) ‘Steddom’ 0.28 b 43.22 ab 2.96 a ‘Thomas’ 0.45 b 56.76 a  3.59 a ‘Spencer’  1.33 ab 38.58 ab  2.78 ab ‘Parida’ 2.11 a 21.42 b  1.73 b ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 9 Tree rating, September 2002 Tree rating Trunk Canopy Fruit rating (0-5; diam vol (0-5; Rootstocks 5 = dead) (cm) (cu ft) 5-heavy) ‘Steddom’ 0.28 c  5.58 a 197.9 a 1.56 a ‘Thomas’ 0.64 bc 6.55 a 277.6 a  0.73 ab ‘Spencer’ 2.06 ab 3.31 b 105.6 b 0.33 b ‘Parida’ 2.39 a  3.44 b 102.4 b 0.11 b Salt rating Canker rating No. trees Rootstocks (0-5; 5 = severe) (0-5; 5 =severe) dead ‘Steddom’ 0.18 c  0.00 a 1/18 ‘Thomas’ 1.05 a  0.00 a 1/11 ‘Spencer’ 0.38 bc 0.00 a 6/18 ‘Parida’ 0.73 ab 0.62 a 6/18

TABLE 10 Tree rating, August 2003. Four-ear trial to-date Tree rating Trunk Canopy Fruit rating (0-5; diam vol (0-5; Rootstocks 5 = dead) (cm) (cu ft) 5-heavy) ‘Steddom’ 0.11 b 7.79 a 419.72 a 1.14 a ‘Thomas’ 0.82 b 7.38 a 417.59 a  0.45 ab ‘Spencer’ 2.39 a 3.72 b 200.02 b 0.17 b ‘Parida’ 2.61 a 3.94 b 186.14 b 0.11 b Salt rating Canker rating Dead trees Rootstocks (0-5; 5 = severe) 0-5; 5 = severe (%) ‘Steddom’ 0.39 b 0.00 a 0 ‘Thomas’ 2.05 a 0.00 a 9 ‘Spencer’ 0.55 b 0.71 a 41 ‘Parida’ 0.28 b 0.40 a 44

TABLE 11 Rootstock rating, December 2003. Three-year trial to-date Tree rating Canopy Trunk Fruit rating (0-5; vol diam (0-5; 5- Rootstocks 5 = dead) (cu ft) (cm) heavy) ‘Zentmyer’ 0.313d 48.0ab 6.45a 1.75abc ‘Merensky II’ 0.556cd 71.6a 6.49a 2.67a ‘Steddom’ 0.677bcd 47.2ab 5.18ab 2.00ab ‘Parida’ 1.147abcd 50.6ab 4.91ab 1.53abcd ‘Evstro’ 1.353abcd 49.6ab 5.55ab 2.29ab ‘Merensky I’ 1.441abcd 48.6ab 5.01ab 1.41bcd ‘Guillemet’ 1.588abc 39.6b 4.58b 0.41d ‘Thomas’ 1.875ab 43.4ab 4.45b 0.72cd ‘UC 2023’ 2.188a 27.2b 4.07b 0.31d ‘VC 207’ 2.382a 32.4b 3.79b 1.12bcd Salt rating Canker rating No. trees Rootstocks (0-5; 5 = severe) (0-5; 5-severe) dead (%) ‘Zentmyer’ 0.00a 0.00a 0 ‘Merensky II’ 0.00a 0.00a 0 ‘Steddom’ 0.00a 0.06a 6 ‘Parida’ 0.00a 0.07a 18 ‘Evstro’ 0.00a 0.06a 0 ‘Merensky I’ 0.00a 0.06a 18 ‘Guillemet’ 0.00a 0.08a 22 ‘Thomas’ 0.00a 0.08a 29 ‘UC 2023’ 0.08a 0.00a 19 ‘VC 207’ 0.00a 0.00a 35 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 12 Rootstock ratings of avocado trees planted in root rot soil at Escondido, July 2002 Tree rating Canopy Trunk Fruit set 0-5; volume diameter rating 0-5; Rootstocks 5 = dead Cu ft Cm 5 = heavy ‘Zentmyer’ 0.00c 397.4abc 7.12bcd 1.53cd ‘Rio Frio’ 0.00c 313.5cdef 6.33cdef 2.13bcd ‘Merens I’ 0.00c 543.6a 8.74a 3.50a ‘Merensk II’ 0.02c 409.0abc 7.81abc 2.84ab ‘VC 241’ 0.06c 238.4defg 6.19defg 1.41cd ‘Uzi’ 0.29bc 504.3ab 8.57ab 2.76ab ‘Steddom’ 0.36bc 376.1bcde 7.07bcd 2.43bc ‘Thomas’ 0.44bc 388.5bcd 6.75cde 1.12de ‘Guillemet’ 0.59bc 192.0fgh 4.90fgh 1.12de ‘Spencer sdlg’ 0.63bc 225.8efg 5.24efgh 1.56cd ‘Leo’ 0.67bc 288.2cdef 5.89defgh 1.60cd ‘Spencer clonal’ 0.69bc 163.8fgh 4.65gh 1.54cd ‘Duke 7’ 1.00b 129.3gh 4.38h 1.47cd ‘G755A’ 0.16b 294.1cdef 5.86defgh 1.56cd ‘PolyN’ 4.12a 65.6h 1.26i 0.24e Tip Burn Cankers Dead Rootstocks Number trees affected ‘Zentmyer’ 0 0 0/15 ‘Rio Frio’ 0 0 0/16 ‘Merens I’ 0 0 0/14 ‘Merensk II’ 0 1 0/17 ‘VC 241’ 0 0 0/16 ‘Uzi’ 2 0 1/17 ‘Steddom’ 0 0 1/14 ‘Thomas’ 0 0 1/17 ‘Guillemet’ 3 1 2/17 ‘Spencer sdlg’ 0 0 2/16 ‘Leo’ 0 0 2/15 ‘Spencer clonal’ 0 0 5/16 ‘Duke 7’ 0 0 3/15 ‘G755A’ 2 1 3/16 ‘PolyN’ 0 0 14/17 

TABLE 13 Rootstock trial tree ratio April 2003¹. Four-year trial to-date Tree rating Canopy volume Trunk diam. Rootstock (0-5;5 = dead) (cu ft) (cm) Salt ‘MerenI’ 0.00d 551ab   10.7a 0.08cd ‘VC241’ 0.06d 281efgh 8.0abc 0.03cd ‘Rio Frio’ 0.07d 362efcd 8.7abc 0.00d ‘Zentmyer’ 0.07d  410bcde 9.2ab 0.32bc ‘MerenII’ 0.18d 532abc  9.4ab 0.21dc ‘Spen sdlg’ 0.36d 263efgh 6.9bc 0.00d ‘Uzi’ 0.38d 669a   10.6a 0.68a ‘Steddom’ 0.39d 478bcd  8.6abc 0.32bc ‘Thomas’ 0.47cd 367cdef 8.4abc 0.62ab ‘Leo’ 0.77cbd 274efgh 7.3abc 0.13cd ‘Guillemet’ 0.83cbd 190ghi  6.2bc 0.13cd ‘Duke 7’ 1.34cb 127hi  8.8abc 0.16cd ‘Spen cl’ 1.44b 211fghi 5.3c 0.12cd ‘G755A’ 1.69b 322defg 7.0bc 0.25cd ‘PolyN’ 4.15a 77i  1.5d 0.06cd Canker Fruit Dead trees Rootstock (0-5; 5 = heavy) rating² (%) ‘MerenI’ 0a 2.97abc 0 ‘VC241’ 0a 3.41ab 0 ‘Rio Frio’ 0a 3.73a 0 ‘Zentmyer’ 0a 3.71a 0 ‘MerenII’ 0.1a   2.97abc 0 ‘Spen sdlg’ 0a 3.57ab 7 ‘Uzi’ 0a 3.47ab 6 ‘Steddom’ 0a 3.75a 7 ‘Thomas’ 0a 3.53ab 6 ‘Leo’ 0a 3.29ab 13 ‘Guillemet’ 0a 2.90abc 13 ‘Duke 7’ 0a 1.53de 19 ‘Spen cl’ 0a 2.35bcd 23 ‘G755A’ 0a 1.78cd 25 ‘PolyN’ 0a 0.29e 82 ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test. ²Fruit was rated in November 2003.

TABLE 14 Temecula, yield 2003^(1;2). Four year trial to-date. Fruit weight/ Number Fruit Rootstock tree (kg) fruit/tree weight (kg) ‘Zentmyer’ 15.89a 68.64a 0.219a ‘Uzi’ 13.99ab 59.24ab 0.195ab ‘Spencer seedling’ 12.52ab 56.27ab 0.181ab ‘Merensky II’ 11.83ab 51.12ab 0.185ab ‘Rio Frio’ 10.87abc 51.33ab 0.187ab ‘Steddom’ 10.01abc 46.20abc 0.175abc ‘Thomas’ 8.50abcd 40.12abcd 0.154abc ‘G755A’ 8.08abcd 34.56abcd 0.116bc ‘VC241’ 7.44bcd 31.75bcd 0.202ab ‘Guillemet’ 7.42bcd 30.00bcd 0.196ab ‘Spencer clonal’ 6.99bcd 32.00bcd 0.136abc ‘Merensky I’ 6.95bcd 32.08bcd 0.148abc ‘Leo’ 6.53bcd 28.14bcd 0.140abc ‘Duke 7’ 3.33cd 14.81cd 0.138abc ‘PolyN’ 1.72d 5.71d 0.076c ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test. ²Only fruit which were grade size were picked; remaining fruit on trees to be picked later.

TABLE 15 Tree rating February 2002¹ Tree rating Fruit set Canopy Trunk No. (0-5; rating (0-5; volume diameter trees Rootstocks 5 = dead) 5 = heavy) (cu ft) (cm) dead ‘Parida’ 1.00 b 0.00 a 13.63 a 2.37 a 0 ‘Steddom’ 1.30 b 0.10 a 18.46 a 2.54 a 0 ‘Afek’  1.50 ab 0.00 a 21.16 a 2.59 a 0 ‘Thomas’ 2.13 a 0.05 a 15.90 a 2.41 a 1 ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test

TABLE 16 Tree rating, March 2003¹. Two-year trial to-date. Tree rating Canopy Trunk Salt tip Canker Dead (0-5; = vol diam 0-5;5 = (0-5;5 = trees Rootstock dead) (cu ft) (cm) severe) severe (%) ‘Steddom’ 0.92 a 61.93 a 4.25 ab 0.61 b 0.00 a 5 ‘Afek’ 1.08 a 72.04 a 4.85 a  1.50 a 0.33 a 0 ‘Parida’ 1.30 a 44.31 a 3.91 ab 0.47 b 0.44 a 10 ‘Thomas’ 1.95 a 39.86 a 3.43 b  1.85 a 0.47 a 15 ¹Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test

TABLE 17 Escondido, Tree ratings, July 2002 Tree rating Canopy Trunk No. No. trees (0-5; vol. diam trees w/tip No. trees Rootstock 5 = dead) (cu ft) (cm) Dead burn w/canker ‘Uzi’ 0.039 b 34.69 a 2.43 a 0 6 0 ‘Guillemet’ 0.042 b 22.86 a 2.06 a 0 4 0 ‘Zentmyer’ 0.077 b 22.40 a 2.25 a 0 2 0 ‘Spencer sdlg’ 0.536 b 27.81 a 2.01 a 0 2 1 ‘Steddom’ 0.615 b 18.93 a 1.99 a 1 0 0 ‘Berg’ 0.714 b 21.42 a 1.98 a 0 1 2 ‘Merensky II’ 0.750 b 32.07 a 2.10 a 2 0 1 ‘Elinor’ 0.786 b 29.44 a 2.03 a 1 0 2 ‘Thomas’ 0.846 b 23.07 a 1.85 a 1 2 0 ‘Pond’  1.00 ab 30.55 a 2.15 a 1 0 2 ‘Crowley’ 1.083 ab 23.78 a 1.86 a 2 1 0 ‘G755A’ 1.231 ab 22.64 a 1.85 a 2 0 0 ‘Duke 9’ 2.270 a   9.40 a 1.07 b 5 0 0 There were significant differences at P = 0.01 between blocks for all tree parameters analyzed.

TABLE 18 Tree ratings, April 2003. Two-year trial to-date. Tree rating Canopy Trunk Fruit rating (0-5; vol diam (0-5; Rootstock 5 = dead) (cu ft) (cm) 5 = heavy) ‘Uzi’ 0.267 c 88.76 a 4.193 a 0.0 a ‘Berg’ 0.531 c 44.16 a 2.956 bc 0.0 a ‘Zentmyer’ 0.600 c 54.37 a 3.393 ab 0.0 a ‘Merensky II’ 0.833 bc 68.49 a 3.333 ab 0.0 a ‘Steddom’ 0.867 bc 56.42 a 3.127 ab 0.0 a ‘Pond’ 0.906 bc 55.05 a 3.188 ab 0.0 a ‘Spenser 0.906 bc 51.45 a 2.988 bc 0.0 a sdlg’ ‘Crowley’ 0.964 bc 42.05 a 3.021 bc 0.0 a ‘Thomas’ 1.071 bc 49.99 a 2.900 bc 0.0 a ‘Guillemet’ 0.167 abc 43.64 a 2.960 bc 0.1 a ‘Elinor’ 1.393 abc 58.40 a 2.864 bc 0.0 a ‘G755A’ 2.156 ab 44.21 a 2.819 bc 0.0 a ‘Duke 9’ 2.577 a 32.16 a 1.885 c 0.0 a Salt rating Canker rating (0-5; (0-5;5 = No. trees Rootstock 5 = severe) severe) Dead (%) ‘Uzi’ 0.933 ab 0.000 a 0 ‘Berg’ 0.633 abcd 0.000 a 6 ‘Zentmyer’ 1.000 a 0.000 a 7 ‘Merensky II’ 0.154 cd 0.308 a 13 ‘Steddom’ 0.321 bcd 0.286 a 7 ‘Pond’ 0.767 abc 0.200 a 6 ‘Spenser sdlg’ 0.300 bcd 0.200 a 6 ‘Crowley’ 0.083 d 0.000 a 14 ‘Thomas’ 0.731 abc 0.000 a 0 ‘Guillemet’ 0.615 abcd 0.133 a 13 ‘Elinor’ 0.333 bcd 0.167 a 14 ‘G755A’ 0.846 ab 0.077 a 13 ‘Duke 9’ 0.313 bcd 0.500 a 38

TABLE 19 Santa Paula, rootstock rating, December 2002 Tree rating Canopy vol Trunk diam Fruit Rootstock (0-5; 5 = dead) (cu ft) (cm) set ‘McKee’ 0.00 b 51.41 a 3.45 bc 0.00 a ‘Merensky II’ 0.00 b 53.45 a 3.66 ab 0.00 a ‘Pond’ 0.00 b 55.08 a 3.69 a 0.00 a ‘Guillemet’ 0.00 b 37.98 b 2.71 f 0.00 a ‘Zentmyer’ 0.00 b 51.92 a 3.38 cd 0.00 a ‘Thomas’ 0.00 b 36.66 b 3.15 de 0.00 a ‘Crowley’ 0.03 b 34.91 b 3.17 d 0.05 a ‘Duke 9’ 0.05 b 31.93 b 2.93 ef 0.00 a ‘Steddom’ 0.27 a 37.14 b 2.75 f 0.00 a Salt burn Trees dead Rootstock (0-5; 5-heavy) Cankers (%) ‘McKee’ 0 0 0 ‘Merensky II’ 0 0 0 ‘Pond’ 0 0 0 ‘Guillemet’ 0 0 0 ‘Zentmyer’ 0 0 0 ‘Thomas’ 0 0 0 ‘Crowley’ 0 0 0 ‘Duke 9’ 0 0 0 ‘Steddom’ 0 0 0 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio.

TABLE 20 Santa Paula, rootstock rating, December 2003. Two-year trial to-date Canopy Trunk Fruit rating Tree rating vol diam (0-5; Rootstock (0-5; 5 = dead) (cu ft) (cm) 5 = heavy) ‘McKee’ 0.025b 184.1b 5.88bc 1.90ab ‘Merensky II’ 0.000b 246.8a  6.18abc 2.60a  ‘Pond’ 0.000b 192.0b 6.24ab 0.00d  ‘Guillemet’ 0.000b  118.8cd 5.38de 0.00d  ‘Zentmyer’ 0.026b 182.8b 6.41a  1.32bc ‘Thomas’ 0.237a 174.9b 5.72cd 0.47cd ‘Crowley’  0.150ab 124.7c 5.42de 2.15ab ‘Duke 9’  0.053ab 132.6c 5.19e  1.89ab ‘Steddom’  0.083ab  86.3d 5.00e  2.00ab Salt burn Trees dead Rootstock (0-5; 5-heavy) Cankers (%) ‘McKee’ 0 0 0 ‘Merensky II’ 0 0 0 ‘Pond’ 0 0 0 ‘Guillemet’ 0 0 0 ‘Zentmyer’ 0 0 0 ‘Thomas’ 0 0 0 ‘Crowley’ 0 0 0 ‘Duke 9’ 0 0 0 ‘Steddom’ 0 0 0 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test.

TABLE 21 Temecula rootstock ratings, Sept 2002 Tree rating Canopy Trunk Fruit rating (0-5; vol. diam (0-5; Rootstock 5 = dead) (cu ft) (cm) 5 = heavy) ‘Zentmyer’ 0.400 c 40.70 ab 2.79 a 0.00 b ‘Crowley’ 0.618 c 40.38 ab 2.86 a 0.00 b ‘Elinor’ 0.824 c 40.52 ab 2.54 a 0.00 b ‘Guillemet’ 0.882 bc 39.13 ab 2.42 a 0.00 b ‘Steddom’ 0.969 bc 29.20 bc 2.13 ab 1.16 a ‘Thomas’ 0.969 bc 31.46 bc 2.13 ab 0.00 b ‘Pond’ 1.088 bc 54.08 a 2.78 a 0.00 b ‘Uzi’ 1.188 bc 35.08 ab 2.56 a 0.00 b ‘G755A’ 2.088 ab 37.85 ab 2.41 a 0.00 b ‘Spencer 2.906 a 11.96 c 1.39 b 0.00 b sdlg’ Salt damage Cankers No. trees Rootstock (0-5; 5 = heavy) (0-5; 5 = heavy) dead ‘Zentmyer’ 1.50 ab 0.00 a 0/15 ‘Crowley’ 1.34 b 0.00 a 1/17 ‘Elinor’ 1.59 ab 0.00 a 1/17 ‘Guillemet’ 1.41 b 0.00 a 2/17 ‘Steddom’ 1.54 ab 0.50 a 2/16 ‘Thomas’ 1.50 ab 0.00 a 3/16 ‘Pond’ 1.40 b 0.00 a 2/17 ‘Uzi’ 1.64 ab 0.00 a 2/16 ‘G755A’ 2.50 ab 0.36 a 4/17 ‘Spencer sdlg’ 2.63 a 0.00 a 4/16

TABLE 22 Temecula, rootstock ratings, December 2003. Two-year trial to-date Tree rating Canopy Trunk Fruit rating (0-5; vol diam (0-5; Rootstock 5 = dead) (cu ft) (cm) 5 = heavy) ‘Zentmyer’ 0.313c  207.27a 6.23a 2.063a ‘Pond’ 0.906c  307.04a 5.75a 1.813a ‘Elinor’ 0.912c  170.37a  4.80a. 1.059a ‘Guillemet’ 1.059c  199.37a 5.73a 0.882a ‘Uzi’ 1.094bc 206.04a 4.35a 0.813a ‘Crowley’ 1.250bc 144.14a 5.04a 1.438a ‘Steddom’ 1.281bc 254.94a 4.89a 1.188a ‘Thomas’ 1.313bc 226.39a 5.16a 1.375a ‘G755A’ 2.438ab 175.55a 5.23a 0.625a ‘Spencer sdlg’ 2.813a   42.12a 2.26a 0.519a Salt damage Cankers Trees dead Rootstock (0-5; 5 = heavy) (0-5; 5 = heavy) (%) ‘Zentmyer’ 1.188ab 0.000a 0 ‘Pond’ 0.321cd 0.000a 13 ‘Elinor’ 0.469cd 0.000a 6 ‘Guillemet’  0.893abc 0.000a 18 ‘Uzi’  0.769abcd 0.000a 19 ‘Crowley’  0.731abcd 0.000a 19 ‘Steddom’ 0.167d  0.000a 25 ‘Thomas’ 1.308a  0.000a 19 ‘G755A’ 1.167ab 0.000a 25 ‘Spencer sdlg’  0.500bcd 0.000a 44

TABLE 23 Rootstock rating, December 2003. On-Year trial to-date Trunk Canopy Tree rating diam vol Fruit rating Rootstocks (0-5; 5 = dead) (cm) (cu ft) (0-5; 5-heavy) ‘Steddom’ 0.050b 3.171a 47.54a 1.353a ‘VC801’ 1.750a 2.628a 38.08a 0.556a ‘Thomas’ 2.688a 1.800b 17.35b 0.063a Salt ratin Canker rating No. trees Rootstocks (0-5; 5 = severe) (0-5; 5 = severe) dead (%) ‘Steddom’ 0.088a 0.000a 0 ‘VC801’ 0.000a 0.000a 38 ‘Thomas’ 0.100a 0.000a 11 Mean values in each column followed by identical letters are not statistically different according to Waller's k-ratio t test. 

What is claimed is:
 1. A new and distinct rootstock variety of avocado tree having the characteristics substantially as described and illustrated herein. 